OPTICAL COMPONENT MADE OF QUARTZ GLASS FOR USE IN ArF EXCIMER LASER LITHOGRAPHY AND METHOD FOR PRODUCING THE COMPONENT

ABSTRACT

An optical component made of synthetic quartz glass includes a glass structure substantially free of oxygen defect sites and having a hydrogen content of 0.1×10 16  to 1.0×10 18  molecules/cm 3 , an SiH group content of less than 2×10 17  molecules/cm 3 , a hydroxyl group content of 0.1 to 100 wt. ppm, and an Active temperature of less than 1070° C. The optical component undergoes a laser-induced change in the refractive index in response to irradiation by a radiation with a wavelength of 193 nm using 5×10 9  pulses with a pulse width of 125 ns and a respective energy density of 500 μJ/cm 2  at a pulse repetition frequency of 2000 Hz. The change totals a first measured value M 193 nm  when measured using the applied wavelength of 193 nm and a second measured value M 633 nm  when measured using a measured wavelength of 633 nm. The ratio M 193 nm /M 633 nm  is less than 1.7.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Division of co-pending U.S. patent applicationSer. No. 14/769,382 filed Aug. 20, 2015, which was a Section 371 ofInternational Application No. PCT/EP2014/053199, filed Feb. 19, 2014,which was published in the German language on Aug. 28, 2014, underInternational Publication No. WO 2014/128148 A3 and the disclosure ofwhich is incorporated herein by reference.

BACKGROUND OF THE INVENTION

Optical components made of synthetic quartz glass and a method forproducing the same are known from WO 2009/106134 A1. The opticalcomponent has a glass structure which is substantially free fromchlorine, oxygen defect sites and SiH groups (below the detection limitof 5×10¹⁶ molecules/cm³). Within a diameter of 280 mm (CA area), thecomponent exhibits a mean hydrogen content of about 3×10¹⁶ molecules/cm³and a hydroxyl group content of 25 wt. ppm.

For the production of the component, a SiO₂ soot body is dried such thata mean hydroxyl group content of less than 60 wt. ppm is obtained in thequartz glass produced therefrom. Prior to vitrification, the soot bodyis subjected to a conditioning treatment including a treatment withnitrogen oxide. For reducing mechanical stresses, the quartz glass blankis subjected to an annealing temperature and is finally loaded withhydrogen in an atmosphere of 80 vol.-% nitrogen and 20 vol.-% hydrogenat 400° C. at an absolute pressure of 1 bar for a duration of 80 hours.

Due to the manufacturing process, the synthetic quartz glass produced inthis way contains nitrogen, which is chemically bound in the glassnetwork. It shows an advantageous damage behavior vis-à-vis shortwave UVlaser radiation especially with respect to the so-called “compaction”.

With the damage behavior of the “compaction”, a local increase indensity is observed in the volume penetrated by radiation during orafter high-energy UV laser irradiation of the glass. This causes a localincrease in the refractive index which is progressing during continuousirradiation and thereby leads to an increasing deterioration of theimaging properties of the optical component and, in the end, to apremature failure of the component.

For the sake of simplicity, the changes in the refractive indexdistribution due to compaction are often determined not at the appliedwavelength, e.g. at 193 nm, but by using a Fizeau interferometerequipped with a helium-neon laser with a measurement wavelength of 633nm (more exactly: at a wavelength of 632.8 nm).

It has now been found that, despite identical or similar measured valuesof their compaction at a measurement wavelength of 633 nm, quartzglasses can surprisingly show different damage behaviors at ameasurement wavelength at 193 nm. This particularly poses problemswhenever the quartz glass to be measured hints at a quite acceptablecompaction behavior at a measurement wavelength of 633 nm, but, upon usewith the applied wavelength, unexpectedly shows much poorer values or iseven unusable.

BRIEF SUMMARY OF THE INVENTION

It is an objective of the present invention to provide an opticalcomponent for use in ArF excimer laser lithography with an appliedwavelength of 193 nm, wherein the component, starting from a measurementof the compaction behavior at a measurement wavelength of 633 nm,permits a reliable prediction of the compaction behavior during use withUV laser radiation of the applied wavelength.

Furthermore, it is an objective of the present invention to provide amethod which is suited for producing such an optical component.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofthe invention, will be better understood when read in conjunction withthe appended drawings. For the purpose of illustrating the invention,there are shown in the drawings embodiments which are presentlypreferred. It should be understood, however, that the invention is notlimited to the precise arrangements and instrumentalities shown.

FIG. 1 shows a diagram in which the ratio of measured values (namely themaximum refractive-index increase) of a damage by compaction is plottedagainst the irradiation dose upon measurement with a measurementwavelength of 193 nm and with a measurement wavelength of 633 nm;

FIG. 2 shows a diagram in which the ratio M_(193 nm)/M_(633 nm)determined on the basis of a model calculation is plotted againstmeasured values of the ratio; and

FIG. 3 shows a result of the model calculation which illustrates thedependence of the ratio M_(193 nm)/M_(633 nm) on the hydrogen content ofthe quartz glass and the hydrogen loading temperature in athree-dimensional representation.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the present invention relates to an optical componentmade of synthetic quartz glass for use in ArF excimer laser lithographywith an applied wavelength of 193 nm, with a glass structuresubstantially without oxygen defect sites, a hydrogen content in therange of 0.1×10¹⁶ molecules/cm³ to 1.0×10¹⁸ molecules/cm³ and a contentof SiH groups of less than 2×10¹⁷ molecules/cm³ and with a content ofhydroxyl groups in the range between 0.1 and 100 wt. ppm, wherein theglass structure has a fictive temperature of less than 1070° C. Anotherembodiment of the present invention relates to a method for producingsuch an optical component.

The glass structure of the optical component according to the presentinvention preferably reacts to irradiation with radiation of awavelength of 193 nm with 5×10⁹ pulses with a pulse width of 125 ns andan energy density of 500 μJ/cm² each time and a pulse repetitionfrequency of 2000 Hz with a laser-induced refractive-index change, theamount of which upon measurement with the applied wavelength of 193 nmyields a first measured value M_(163nm) and upon measurement with ameasurement wavelength of 633 nm a second measured value M_(633 nm),where: M_(193 nm)/M_(633 nm)<1.7.

The dose of irradiation with radiation of the applied wavelength isdefined by the pulse number of the laser pulses, their pulse width andenergy density and the pulse repetition frequency. With this irradiationdose, the component according to the invention exhibits a compactionbehavior with the following typical features:

-   (a) After the above-specified irradiation dose, the respective    measured values M_(193 nm) and M_(633 nm) of the measurements of the    compaction behavior at 193 nm and at 633 nm show a ratio    M_(193 nm)/M_(633 nm) that is smaller than 1.7. This is a    comparatively small ratio M_(193 nm)/M_(633 nm). It has been found    that the small ratio represents not only a high compaction    resistance of the glass, but is also an indispensable condition for    the predictability of the compaction itself-   (b) It has been found that in the quartz glass according to the    invention, this small ratio of M_(193 nm)/M_(633 nm) which satisfies    condition (a) remains almost constant, even if the irradiation dose    exceeds the above-specified dose. In view of the constant ratio, it    is possible to calculate the compaction due to irradiation with the    applied wavelength also for every higher radiation dose than the    above-specified one in an exact manner or at least with sufficient    accuracy, namely on the basis of a measurement at 633 nm.

If the fulfillment of condition (a) is known for sure, it is thuspossible due to condition (b) to reliably predict, by measurements at awavelength of 633 nm, the compaction behavior upon use of the quartzglass with UV laser radiation of 193 nm. The glass structure issubstantially free of oxygen defect sites, such that the concentrationsof oxygen deficient defects and oxygen excess defects in the glassstructure are below the detection limit of the Shelby method.

The Shelby detection method is published in “Reaction of hydrogen withhydroxyl-free vitreous silica” (J. Appl. Phys., Vol. 51, No. 5 (May1980), pp. 2589-2593). Quantitatively, this results in a number ofoxygen deficient defects or oxygen excess defects in the glass structureof not more than about 10¹⁷ per gram quartz glass.

On the basis of this method, the content of SiH groups is alsodetermined, with a calibration being carried out on the basis of thechemical reaction: Si—O-Si+H₂→Si-H+Si-OH. SiH groups and hydrogen are ina mutual thermodynamic equilibrium. The content of SiH groups is lessthan 2×10¹⁷ molecules/cm³ in the quartz glass of the component accordingto the invention, and the hydrogen content is in the range of 0.1×10¹⁶molecules/cm³ to 1.0×10¹⁸ molecules/cm³.

Hence, SiH— groups are formed by reaction with molecular hydrogen withbreakdown of the SiO₂ network. They are not desired because a so-calledE′ center and atomic hydrogen may evolve from them upon irradiation withenergy-rich UV light. The E′ center causes an increased absorption at awavelength of 210 nm and is also disadvantageously noticed in theneighboring UV wavelength range.

The hydrogen content (H₂) content is determined with the help of a Ramanmeasurement, as suggested in “Khotimchenko et al.; Determining theContent of Hydrogen Dissolved in Quartz Glass Using the Methods of RamanScattering and Mass Spectrometry,” Zhurnal Prikladnoi Spektroskopii,Vol. 46, No. 6 (June 1987), pp. 987-991.

The content of hydroxyl groups is in the range between 0.1 and 100 wt.ppm, preferably between 10 and 60 wt. ppm. The hydroxyl group content isobtained from the measurement of the IR absorption according to themethod of D. M. Dodd et al. (see, e.g., “Optical Determinations of OH inFused Silica”, (1966), pp. 3911).

With a decreasing hydroxyl group content, the viscosity of quartz glassis increasing. The low hydroxyl group content of less than 100 wt. ppmleads to a more rigid glass structure and improves the behavior toward alocal anisotropic density change, particularly in the case of linearlypolarized UV radiation. It has also been assumed that the density changeupon compaction is accompanied by a rearrangement of hydroxyl groups,this rearrangement mechanism being the more likely and easier, the morehydroxyl groups are available.

The fictive temperature of the glass structure is less than 1070° C.,preferably less than 1055° C. Its measurement method, based on ameasurement of the Raman scattering intensity at a wave number of about606 cm⁻¹, is described “The UV-induced 210 nm absorption band in fusedSilica with different thermal history and stoichiometry,” Ch. Pfleidereret. al., J. Non-Cryst. Solids 159 (1993) 145-143.

The content of fluorine is preferably less than 10 wt. ppm and thecontent of chlorine is preferably less than 0.1 wt. ppm. Halogens mayreact with the SiO₂ glass network with breakdown and can thereby weakenthe network.

It has been found that the predictability of the compaction behaviorupon use of the quartz glass with UV laser radiation of 193 nm is morereliable by measurement at a wavelength of 633 nm, as the ratio of firstand second measured value is relatively smaller.

Therefore, in a preferred embodiment of the component, upon measurementof the laser-induced refractive index change, the following isapplicable to the ratio of the first measured value M_(193 nm) and thesecond measured value M_(633 nm):M_(193 nm)/M_(633 nm)<1.6, and morepreferably M_(193 nm)/M_(633 nm)<1.55.

In one embodiment according to the invention, a method for producing theoptical component comprises:

-   a) producing a porous soot body of SiO₂ by flame hydrolysis of a    silicon-containing start sub stance,-   b) drying the soot body,-   c) treating the soot body in an oxidizing atmosphere containing N₂O,    with the proviso that a hydroxyl group content is set in the soot    body by drying according to method step (b) and by treatment    according to method step (c) in such a manner that due to-   d) subsequent sintering of the soot body, a semifinished product of    quartz glass is obtained that has a mean hydroxyl group content in    the range between 0.1 and 100 wt. ppm,-   e) shaping the semifinished product into a blank of quartz glass and    annealing the blank, such that the blank has a mean fictive    temperature of less than 1070° C., and-   f) loading the blank with hydrogen by heating in a    hydrogen-containing atmosphere at a temperature below 400° C. while    producing a mean hydrogen content in the range of 0.1×10¹⁶    molecules/cm³ to 1.0×10¹⁸ molecules/cm³.

The quartz glass for the optical component according to the invention isproduced according to the so-called “soot method”. A porous body of SiO₂soot (here called “soot body”) is obtained as an intermediate product.The porosity of the soot body makes it possible to change the chemicalcomposition, and thus also directly the SiO₂ network structure, and toadapt it to special demands. Specifically, the concentrations ofhydroxyl groups and halogens can be reduced and set to predeterminedvalues, or components such as oxygen or nitrogen may be added.

Drying of the soot body is carried out by heating below thevitrification temperature either in a halogen-containing atmosphere or,preferably, under vacuum. Drying leads to a reduction of the hydroxylgroups, which are contained in the soot body due to the manufacturingprocess, to the predetermined value. The reduction is preferably asuniform as possible. Ideally, the subsequent treatment steps no longerhave any significant influence on the hydroxyl group content.

A treatment step of the porous body in an oxidizing atmospherecontaining N₂O is essential for the compaction behavior of the quartzglass. Dinitrogen monoxide (N₂O) decomposes at a high temperature intooxygen and reactive nitrogen atoms and compounds that are able to reactwith and saturate the defect sites of the quartz-glass networkstructure, thereby eliminating the defect sites. The glass network isthereby strengthened.

Apart from the oxidative treatment with N₂O, after-treatments of thequartz glass blank obtained from the soot body after vitrification makea further substantial contribution to this effect. On the one hand, amean fictive temperature of less than 1070° C. is set by annealing theblank; on the other hand, the blank is loaded with hydrogen by heatingin a hydrogen-containing atmosphere.

Subsequently, the soot body is vitrified under vacuum into a cylindricalquartz-glass blank. Molecular hydrogen which is introduced into thequartz glass in the flame hydrolysis method and which otherwise wouldfurther react forming undesired SiH groups in the subsequent hottreatment steps is removed by the vacuum.

After vitrification, a quartz glass blank with a hydroxyl group contentranging between 0.1 and 100 wt. ppm is obtained. The quartz glass blankis substantially free of SiH groups and of hydrogen (i.e., the contentof the two components is below the detection limit).

To reduce mechanical stresses as well as birefringence and to produce acompaction-resistant glass structure, the quartz glass blank issubjected to an annealing treatment which is carried out such that,measured over the volume, a mean fictive temperature of less than 1070°C., preferably less than 1055° C., is obtained. It has been found that acomparatively dense network structure is thereby produced, whichcounteracts further (local) compaction by UV radiation.

The defect-healing action of hydrogen is known. Therefore, depending onthe application and on the projected service life of an opticalcomponent, a certain hydrogen content is often predetermined, even ifother disadvantages have to be accepted in return. After annealing, thehydrogen content of the quartz glass is, however, below the resolutionlimit of the measurement method. The quartz glass is subsequently loadedwith hydrogen. Preferably, the loading with hydrogen is carried out at atemperature below 400° C., preferably below 350° C., because in athermodynamic equilibrium, SiH groups are formed at elevatedtemperatures in the quartz glass at the presence of hydrogen at elevatedtemperatures. The particularly low loading temperature prevents oravoids this. Upon irradiation with energy-rich UV light, SiH groups mayform so-called E′ centers which, in turn, cause an enhanced absorptionat a wavelength of 210 nm, which can be disadvantageously noticed alsoin the neighboring wavelength range of the applied radiation.

A mean hydrogen content in the range of 0.1×10¹⁶ molecules/cm³ to1.0×10¹⁸ molecules/cm³ is set. Due to the low loading temperature, ahigh hydrogen partial pressure is instrumental in achieving an adequatehydrogen loading within economically reasonable treatment periods. Thehydrogen partial pressure is therefore preferably between 1 and 150 bar.

An increased pressure accelerates not only hydrogen loading, but mayalso contribute to a somewhat compacter glass structure of increaseddensity that is resistant to local anisotropic density change.

The outcome of the manufacturing method is a cylinder of quartz glasswith a specific compaction behavior. After irradiation with the specificradiation dose of the wavelength of 193 nm (with 5×10⁹ pulses with apulse width of 125 ns and an energy density of 500 μJ/cm² each time anda pulse width repetition frequency of 2000 Hz), the quartz glass reactswith a maximum value of the laser-induced refractive index change, theamount of which upon measurement with the applied wavelength of 193 nmyields a first measured value M_(193 nm) and upon measurement with ameasurement wavelength of 633 nm yields a second measured valueM_(633 nm), where M_(193 nm)/M_(633 nm)<1.7; and preferably,M_(193 nm)/M_(633 nm) is less than 1.6, and more preferablyM_(193 nm)/M_(633 nm) is less than 1.55.

It is important, particularly at a sufficiently small ratio value, thatthe ratio remains constant upon further irradiation under the sameirradiation conditions, which permits a reliable prediction of thedamage upon further irradiation with the applied radiation, based on ameasurement at 633 nm.

The level of the constant value of the ratio M_(193 nm)/M_(633 nm) isparticularly strongly influenced by the maximum loading temperature inthe hydrogen treatment and by the mean hydrogen concentration producedthereby in the quartz glass. The hydrogen loading temperature can beregarded as a measure of the number of defect sites and SiH groups.

The optical component for use in microlithography for the appliedwavelength of 193 nm is obtained from the quartz glass cylinder bystandard after-treatment steps, such as cutting, grinding, polishing.

To avoid contact of the SiO₂ network with halogen-containing dryingreagents, the drying of the soot body according to method step (b) ispreferably carried out purely thermally under vacuum or in inert gas,and comprises a treatment of the soot body at a drying temperature inthe range between 100° C. and 1350° C., preferably at not more than1300° C.

An input of halogens into the soot body is avoided by dispensing withhalogen-containing drying reagents, so that these do not have to beremoved again later. On the other hand, oxygen defects are created dueto the long-winded thermal treatment under reducing conditions, becausea suitable substituent is not directly available for the removed OHgroups. The oxygen defects impair the UV radiation resistance of thequartz glass.

Accordingly, after completion of the drying treatment, the soot body istreated in N₂O-containing atmosphere at the same or a lower temperature.Treatment temperatures of less than 600° C., preferably below 500° C.,are particularly useful. The N₂O content of the atmosphere is between0.1 and 10 vol.-%, preferably between 0.5 and 5 vol.-%; the treatmentduration is at least 10 h.

At nitrogen oxide contents below 0.1 vol.-%, a small oxidative effect isachieved, and at nitrogen oxide contents of more than 10 vol.-%, theSiO₂ network may be overloaded with nitrogen and bubbles may form in thesubsequent vitrification. The treatment is carried out at such a lowtemperature that the porosity of the soot body is maintained. Attreatment temperatures of less than 200° C., the reactivity of N₂O ishowever very low and long treatment periods are needed for achieving anoticeable effect with respect to the saturation of oxygen defects.

Sample Preparation

A soot body is produced by flame hydrolysis of SiCl₄ and the OVD method.The soot body is dehydrated under vacuum at a temperature of 1200° C.for 50 hours in a heating furnace having a heating element of graphite.The graphite in the heating furnace produces reducing conditions. If thesoot body is immediately vitrified after this treatment stage, quartzglass that includes oxygen defects in the order of 1.7×10¹⁶ cm⁻³ areobtained.

The thermally dried soot body is subsequently heated in an oxidizingatmosphere. The soot body is continuously heated in a treatment chamberwith a treatment gas of dinitrogen monoxide (N₂O; 1.5 vol.-%) in acarrier gas stream of nitrogen to a temperature of 450° C. and kept atthis temperature for 20 hours.

Subsequently, the dried and aftertreated soot body is vitrified in asintering furnace at a temperature of about 1400° C. under vacuum (10⁻²mbar) into a transparent quartz glass blank. The blank is subsequentlyhomogenized by thermo-mechanical homogenization (twisting) and formationof a quartz glass cylinder.

After completion of the homogenization treatment, the hydroxyl groupcontent of the soot body is about 25 wt. ppm.

To reduce mechanical stresses as well as birefringence and to produce acompaction-resistant glass structure, the quartz glass cylinder issubjected to an annealing treatment in which the quartz glass cylinderis heated in air and at an atmospheric pressure to 1190° C. for aholding period of 8 hours and is subsequently cooled at a cooling rateof 4° C./hour to a temperature of 1050° C. and is kept at the lowertemperature for 4 hours. Thereupon, the quartz glass cylinder is cooledat a higher cooling rate of 50° C./hour to a temperature of 300° C.,whereupon the furnace is switched off and the quartz glass cylinder isallowed to cool freely in the furnace.

The quartz glass cylinder treated in this way has an outer diameter of350 mm and a thickness of 60 mm. Measured over the thickness, a meanfictive temperature of 1065° C. is obtained.

The quartz glass cylinder is subsequently loaded with hydrogen. Thetwo-stage treatment is carried out in an atmosphere of 100 vol.-%hydrogen by heating at a temperature T_(loading) of 380° C., first at apressure p1 _(loading) of 11 bar and for a holding period t1 _(loading)of 30 hours, and subsequently at a pressure p2 _(loading) of 1 bar andfor a holding period t2 _(loading) of 80 hours.

The quartz glass cylinder obtained thereafter is substantially free ofchlorine oxygen defect sites and SiH groups (below the detection limitof 5×10¹⁶ molecules/cm³), and is distinguished within a diameter of 280(CA area) by a mean hydrogen content of 40×10¹⁶ molecules/cm³ and ahydroxyl group content of 25 wt. ppm.

Table 1 summarizes the parameters of the individual method steps and themeasurement results for the above-described Sample 1 and for furtherSamples 2 to 7 which are produced in a similar way.

TABLE 1 Sample 1 2 3 4 5 6 7 T_(N2O) treatment (° C.)/  550/20  550/20 550/20 —  450/20 — — t_(N2O) treatment (hours) T1_(annealing) (° C.)/1190/8 1190/8 1190/8 1190/8 1190/8 1190/8 1190/8 t1_(annealing) (hours)T2_(annealing) (° C.)/ 1050/4 1100/4 1050/4 1050/4  980/4 1100/4 1070/4t2_(annealing) (hours) T_(loading) (° C.) 380° C. 400° C. 400 425° C.380° C. 425° C. 450° C. t1_(loading) (hours)/ 30 h @ 50 h @ 30 h @ 30 h@ 30 h @ 15 h @  6 h @ p1_(loading) (bar) 11 bar 100 bar 5 bar 5 bar 11bar 50 bar 11 bar t2_(loading) (hours)/ 80 h @ 70 h @ 70 h @ 70 h @ 80 h@ 70 h @ 70 h @ p2_(loading) (bar) 1 bar 25 bar 0.9 bar 0.9 bar 1 bar 6bar 0.6 bar OH (wt. ppm) 25 21 22 37 35 38 40 Mean value of Tf 1065 11021067 1060 1054 1105 1075 (° C.) Hydrogen cont. 40 850 30 30 40 200 20(×10¹⁶ molecules/cm³) SiH content 6 212 15 20 4 100 20 (×10¹⁶molecules/cm³) M_(193 nm)/ M_(633 nm) 1.55 4.70 1.69 1.75 1.53 15.271.75

Compaction Measurement

All of the Samples 1-7 were irradiated with radiation of a wavelength of193 nm, which is characterized by the following dose:

Pulse number: 5×10⁹ pulses;

Pulse width: 125 ns;

Energy density: 500 μJ/cm² each time; and

Pulse repetition frequency: 2000 Hz.

In the sample irradiated in this way, the amount of the local maximumrefractive-index change as compared with the non-irradiated glass isdetermined, namely both by measurement with a measurement wavelength of193 nm (amount of the maximum refractive-index change: M_(193 nm)) andby measurement with a measurement wavelength of 633 nm (amount of themaximum refractive-index change: M_(633 nm)). The ratio of the measuredvalues M_(193 nm)/M_(633 nm) is indicated in the last row of Table 1.

The measurement results show that the ratio M_(193 nm)/M_(633 nm) can beregarded as a quality reference to a small and predictable compaction,and is obviously considerably determined by the parameters in theafter-treatment of the soot body in a N₂O-containing atmosphere andafter-treatment of the vitrified quartz glass blank in an H₂-containingatmosphere. Also, the intensity of the N₂ treatment for the eliminationof oxygen defect sites and the temperature during hydrogen loading playa decisive role in preventing SiH groups.

This is also demonstrated by the further measurement results discussedhereinafter with reference to the diagrams of FIGS. 1 to 3.

Specifically, for Sample 3, FIG. 1 shows the development of the ratio V(M_(193 nm)/M_(633 nm)) with the irradiation dose (“dose”) as a productof the energy density to the square and pulse number divided by thepulse width in time in ns (in the unit (J/cm²)²/ns).

Thus, the ratio M_(193 nm)/M_(633 nm) first rises steeply at theirradiation beginning from 1.0 to about 1.69, and remains thereafter(after a pulse number of about 3×108 pulses, or after a dose D of about3 J/cm²)²/ns) approximately constant at this value (hereinafter alsocalled “final value”).

Corresponding tests were carried out for other quartz glass qualities.Samples 1 and 5 showed similar profiles of the ratioM_(193 nm)/M_(633 nm) with the irradiation dose. An initially strongerrise of the ratio M_(193 nm)/M_(633 nm) to more than 1.7 was found inthe remaining samples and also a less constant profile with anincreasing irradiation dose. These are comparative samples (i.e.,Samples 2, 4, 6 and 7).

In Samples 1, 3 and 5, due to the substantially constant ratioM_(193 nm)/M_(633 nm), the degree of compaction can be reliablyindicated by continuous measurements at a wavelength of 633 nm by usingthe quartz glass with UV laser radiation of 193 nm.

Based on the results of numerous measurements of such a type, it wasfound that if the quartz glass has been subjected to an adequatelyoxidative treatment under N₂O, the parameters that influence the finalvalue of the ratio can ultimately be summarized in the loadingtemperature in the case of hydrogen loading (T_(loading) in ° C.) and inthe mean hydrogen concentration (C_(H2) in 10¹⁷ molecule/cm³) producedin the quartz glass.

Thus, the temperature during loading of the quartz glass with hydrogenis of relevance to the formation of SiH groups. The lower thetemperature, the lower the SiH group concentration evolving in thethermal equilibrium. On the other hand, hydrogen loading isdiffusion-controlled, so that low loading temperatures, depending on thediffusion length and an acceptable concentration gradient, require longtreatment periods.

The loading process is energy- and time-consuming and, therefore, asshort and “cold” as possible, but must be carried out for such a longperiod as is needed for ensuring a given compaction behavior of thequartz glass. This estimation has so far been an empirical one. However,it has been found that the following equation is suited for estimatingthe final value for the ratio M_(193 nm)/M_(633 nm):

M _(193 nm) /M _(633 nm)=1.47+0.0345×2^(((Tloading−400)/25)) ×C_(H2)  (1)

Thus, at the moment, the final value has a limit of 1.47 that must bereached. Additional contributions are due to the parameters of thehydrogen loading. Based on the calculation model (1), the final valuecan thus be estimated for the ratio M_(193 nm)/M_(633 nm) and thus thecompaction tendency of the quartz glass toward UV radiation of awavelength of 193 nm, particularly in the case of linearly polarizedradiation, and hydrogen loading can thereby be optimized.

The validity of this model assumption is demonstrated by FIG. 2.Referring to FIG. 2, the final value of the ratio M_(193 nm)/M_(633 nm),which is determined on the basis of the above-indicated modelcalculation (1), is plotted for some of the samples of Table 1 againstthe actually-measured final values after irradiation with theabove-specified irradiation dose. The measured values are located almostexactly along a straight line with the slope 1, which can be regarded asproof of the correctness of the model according to equation (1).

The result becomes more comprehensible with a look at thethree-dimensional modeling of FIG. 3. Referring to FIG. 3, the finalvalue of the ratio M_(193 nm)/M₆₃₃ (as a measure of the compactiontendency of the quartz glass) is plotted against the hydrogen content ofthe quartz glass C_(H2) in 10¹⁷ molecules/cm³ (x-axis) and against thetemperature T_(loading) in ° C. with the hydrogen loading (z-axis). Theloading temperature T_(loading) is a measure of the SiH concentration atthe same time.

Thus, the compaction tendency normally increases strongly with theloading temperature and slightly with the hydrogen concentration. Acertain hydrogen concentration is often given. This specification canbasically be met at a high loading temperature within a short period oftime and at a low loading temperature within a longer period of time.For the former, an increased compaction tendency follows automatically;for the latter, there is an economically more troublesome productionprocess.

If, in addition to the hydrogen concentration, the maximally admissiblecompaction tendency is also given, the highest, but still acceptableloading temperature can be determined with the help of the model and theloading period can thus be shortened to a minimum.

It will be appreciated by those skilled in the art that changes could bemade to the embodiments described above without departing from the broadinventive concept thereof. It is understood, therefore, that thisinvention is not limited to the particular embodiments disclosed, but itis intended to cover modifications within the spirit and scope of thepresent invention as defined by the appended claims.

I claim:
 1. An optical component made of synthetic quartz glass for usein ArF excimer laser lithography with an applied wavelength of 193 nm,the optical component comprising: a glass structure which issubstantially free of oxygen defect sites, the glass structure having ahydrogen content in the range of 0.1×10¹⁶ molecules/cm³ to 1.0×10¹⁸molecules/cm³, a content of SiH groups of less than 2×10¹⁷molecules/cm³, a content of hydroxyl groups in the range between 0.1 and100 wt. ppm, and a fictive temperature of less than 1070° C., whereinthe glass structure reacts to irradiation with radiation of an appliedwavelength of 193 nm with 5×109 pulses with a pulse width of 125 ns andan energy density of 500 μJ/cm2 each time and a pulse repetitionfrequency of 2000 Hz with a laser-induced refractive-index change, theamount of which upon measurement with the applied wavelength of 193 nmyields a first measured value M_(193 nm) and upon measurement with ameasurement wavelength of 633 nm yields a second measured valueM^(633 nm), and wherein M_(193 nm)/M_(633 nm)<1.7.
 2. The opticalcomponent according to claim 1, wherein M_(193 nm)/M_(633 nm)<1.6. 3.The optical component according to claim 1, wherein the fictivetemperature is less than 1055° C.
 4. The optical component according toclaim 1, wherein the content of hydroxyl groups is between 10 and 60 wt.ppm.
 5. The optical component according to claim 1, wherein the glassstructure has a content of fluorine of less than 10 wt. ppm.
 6. Theoptical component according to claim 1, wherein the glass structure hasa content of chlorine of less than 0.1 wt. ppm.